1. Technical Field of the Invention
The present invention relates generally to power and control transmission systems, and specifically to, power and control transmission over RF coaxial cables.
2. Description of Related Art
Network analyzers and other types of measuring instruments are used to measure the magnitude and/or phase of a signal present in a device-under-test (DUT). For example, network analyzers can be used to determine the impedance, gain, group delay, gain compression and other characteristics of mobile telecommunications devices, such as base station antennas, amplifiers, cables and attenuators.
To perform a measurement, the instrument is connected to the DUT via one or more couplers that are strategically placed on one or more feeder cables of the DUT. To interface with the DUT, the instrument supplies RF signals, power and control signals to the coupler(s). For example, when using a network analyzer to measure the antenna return loss of a base station antenna, the RF signals can correspond to a swept signal injected into the feeder cable of a base station antenna. If there are any discontinuities in the feeder cable or antenna, part of the signal may be reflected back down the feeder cable to the network analyzer via the coupler. The control signals from the network analyzer control the RF switches in the coupler. For example, the coupler can be programmed to couple forward power, reverse power or calibration path signals to/from the network analyzer depending upon the states (on/off) of the RF switches in the coupler.
Traditionally, each coupler had separate ports for RF signals (injected signal and reflected signal), power and control signals. Likewise, the instrument also had separate ports for each coupler for the RF signals, power and control signals. The RF signal ports of the instrument and coupler were connected together via coaxial cables, while the power and control ports of the instrument and coupler were connected together via one or more multi-conductor cable assemblies. Depending upon the particular DUT, each of the cables used for connecting the instrument to the DUT could potentially be 40 feet long. Such cables are expensive and difficult to install (i.e., each cable may take up to 30 minutes to install). In addition, for outdoor installations, each cable represents a possible point of water ingress into the coupler.
In systems that require only RF signals and power (no control signals), such as high frequency microwave circuit systems, the RF and power signals can be multiplexed onto a single coaxial cable. The RF signals are transmitted over the RF cable and DC power is transmitted over the center conductor of the cable. A bias network on either side of the coaxial cable separates the RF and power signals. For example, a bias network can include a capacitor to block DC power and an inductor to block the RF signals.
However, in systems that require RF signals, power and control signals, there is currently no mechanism for multiplexing the control signals with the power or the RF signals. Therefore, what is needed is a transmission system for RF signals, power and control signals with a reduced amount of cabling.